SURFACE WIND SYSTEMS OVER CENTRAL JAPAN IN THE WARM SEASON-WITH SPECIAL REFERENCE TO THE SOUTHWESTERLY FLOW PATTERN

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In the previous paper, the author analysed the local wind systems in central Japan in winter, from the viewpoint of synoptic climatology, and described their distribution in detail, whose pattern mainly changed corresponding to gradient wind direction and velocity. However, northerly or westerly flow patterns usually prevail over the area in the winter season, and consequently the state of the surface wind systems in the southerly flow pattern could not be obtained. The author is going to discuss this problem in the present paper. The method of arrange-ment of the data is the same as in the previous paper. Firstly, thirty days were selected in the warm season by the following criteria: that the gradient wind blows from a southerly dir-ection at a speed exceeding 10m/s on the surface weather chart, and that the disturbances do not directly affect the area for the whole day. The wind and weather data of about 600 clima-tological stations were inscribed on the maps and the streamlines delineated at 9 a. m. each day. A typical example is shown in Fig. 1. The station is identified by a circle and cloud cover is represented by the symbol adopted by the World Meteorological Organization. The wind is indicated by arrows and the wind force barbs according to the Beauf ort scale. Local wind systems are clearly perceived in various parts of these maps. Especially, south-erly or southwesterly airstreams prevail all along the coast. However, topography features on a meso- or macro-scale, such as mountains, peninsulas, valleys and bays, affect not only the airflow pattern, but weather distribution. For instance, southerly wind, the so-called f oehn, observed in the I-Iokuriku District along the Sea of Japan, is dry and strong, and develops down the lee slope of the mountain range and becomes strongest at the mountain foot, above all at the apex of the fan. Moreover, a clear sky is frequently observed in the lee area, though extensive areas with cloud cover tend to spread over the windward side of the mountain slope. This example shows the most common wind distribution in the southwesterly flow pattern, though, of course, the above-mentioned distribution maps of wind direction are slightly differ ent from each other. Generally speaking, the pattern of wind distribution on these maps is more complicated than that in winter, because the surface wind systems are indirectly influ-enced by disturbances, such as cyclone and front. However, when the gradient wind on the surface weather chart is 180° to 240° and its speed exceeds lOm/s, the maps of streamlines show a similar pattern to each other as shown in Fig. 1 (Wind direction is represented in degrees as measured clockwise from due north.) This flow pattern occurs when an extra-tropical cyclone advances eastward over the northern Japan Sea and Central Japan lies in the rear of a migratory high. This flow pattern is denoted by Type V in accordance with the classification of Types in the previous paper. The other flow patterns in the warm season, such as the southeasterly one, were not analysed in that paper, because their frequency is relatively low and the above-mentioned pattern is dominant. In order to represent schematically the distribution of the surface wind systems for Type V, a composite map of the surface wind distribution was made in the same manner as in the previous paper. Twenty examples were selected for this purpose, which are comprised in the above-cited category. Results are illustrated in Fig. 2. Streamlines of the surface wind are drawn with solid arrows. Broken arrows, however, are used instead in some areas, where the surface wind is so weak or the climatological stations are so sparse that the streamlines are difficult to ascertain, especially owing to their being located at valley bottoms in a mountainous region. Hatched and dotted areas indicate areas with strong and weak wind respectively.
The Association of Japanese Geographersの論文

SURFACE WIND SYSTEMS OVER CENTRAL JAPAN IN THE WARM SEASON-WITH SPECIAL REFERENCE TO THE SOUTHWESTERLY FLOW PATTERN

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